1. Field of the Invention
The present invention relates to a display scrolling circuit suitable for use in game machines and the like wherein images are displayed by a unit of characters or pixels.
2. Description of the Prior Art
In general, display devices used in the game machines and the like are classified into two systems. One of them is a character display system while the other system is a bit map display system.
The character display system displays a picture formed by a combination of characters. When a character to be displayed is specified, the color data of pixels corresponding to that character (e.g., one character being formed by 8 pixels.times.8 pixels) are also specified. On the contrary, the bit map display system directly specifies the color data of each of pixels forming an image. In any event, red-green-blue (RGB) data is finally specified for every scan line on CRT or the like. The color components corresponding to the RGB data for one scan line will be displayed on the display in synchronism with each scan.
The conventional game machines have a function of scrolling the entire display image in the horizontal or vertical direction. An image which can be scrolled may be formed to have a magnitude four times larger than the normal static image, for example. The conventional display circuit scrolls an image on the display by suitably moving an area to be displayed. Such scrolling is performed in the horizontal or vertical direction according to the need. When the scroll is simultaneously made both in the horizontal and vertical directions, the entire image will be diagonally scrolled.
However, the conventional display circuits are adapted to do the same amount of scrolling for the entire display image. Thus, the scroll cannot be variable for every display line. This raised a problem in that the image cannot be eventful by utilizing the scroll.
The inventors found that if the amount of scrolling can be differently set for every line, many kinds of images can be simply formed. If it is now assumed that a straight road extending in the vertical direction is to be displayed, such a road can be deformed into any one of various curved roads by varying the amount of horizontal scrolling for every line.
However, the conventional display circuits could not make such an image display since they could not vary the amount of scrolling for every display line.
Among the commercially available processors, there is a processor to which a graphic controller function is added. When such a processor is used, the scroll can be carried out for every group of lines, relating to one display image. In such a case, the processor must be interrupted each time when the amount of scrolling is changed for every group of lines. After the processor has been interrupted, it will set a new amount of scrolling. This newly set amount of scrolling is used to display a new image. In such a manner, scrolling can be made for every group of lines, as described.
When the processor is interrupted to vary the amount of scrolling for every group of lines, the burden on the processor extremely increases. More particularly, when the processor is interrupted to set a new amount of scrolling, the game computation inherently executed by the processor will be interrupted. If the setting of the amount of scrolling is not terminated until initiation of the next line display, the next line will not be displayed by the proper amount of scrolling. This is undesirable since a flicker is produced on the display.